The invention relates to an apparatus for damping sound in the optical beam path of a microscope, having an acoustic insulation housing (housing) for encapsulating a sound-emitting component, preferably a rapidly moving or oscillating beam deflection means, in particular a resonantly oscillating mirror, the housing comprising at least one optical entrance/exit opening (opening). The invention further relates to a microscope, preferably a scanning microscope, having a corresponding apparatus.
There exist in microscopes, in particular in scanning microscopes, a variety of sound sources, mostly produced by movable components in the optical beam of the microscope. Acoustic emissions are objectionable in the context of operation of the microscope, on the one hand with regard to the person using the microscope and on the other hand with regard to vibrations resulting from the acoustic emission.
In scanning microscopy, a beam deflection device serves for beam control, in particular for incoupling the illumination light, the sample being scanned, for example, line by line in meander fashion by the deflected illumination beam. Detected light returning from the sample passes through the beam deflection device and is guided to the detectors.
In particular with the use of resonant galvanometers, which drive a mirror that moves or is caused to oscillate around its own rotation axis at a frequency of several kHz, unpleasant objectionable noise occurs at high deflection rates, specifically because of the sound proceeding from the movable parts.
The underlying problem here has already been recognized in practice. Reference is made in this regard, merely by way of example, to DE 10 2004 049 437 A1.
Provision is made therein to position the movably arranged deflection means in a very largely soundproof housing having an entrance window and/or an exit window. The sound source is ultimately encapsulated, and the entrance window and/or exit window are to be understood as optical elements that influence the beam path (illumination beam path and/or detected beam path).
The encapsulation known from DE 10 2004 049 437 A1 is problematic in practice, however, since the windows obligatorily necessary therein are undesirable in optical terms. They result in a transmittance of less than 100% and produce not inconsiderable interference at the interfaces. Even if optical components that are in any case necessary in the beam path (for example, lenses) are used as windows, the need for soundproof installation of the movable parts into a housing entails very considerable limitations. Variable components in particular, for example beam splitter sliders, can be arranged only with extreme difficulty inside a hermetically sealed housing, but principally must be operable or actuatable from outside. The design outlay is considerable, if indeed implementation is possible at all.
Be it noted at this juncture that what is important here is essentially the elimination of sound waves that are caused inside a microscope by rapidly moving parts. The beam deflection device utilized in a scanning microscope, with its rapidly moving, usually resonantly operating deflection means, is recited here merely by way of example and serves for discussion of the teaching claimed. Movements, in particular rapid ones, of components, for example of such deflection means, result in any case in undesired emissions of sound. An acoustic emission is perceived to be particularly objectionable when it is caused by a component that is excited to oscillate, resonantly or nonresonantly, in the range of several kHz, as is routinely the case in the context of scanning microscopy when the mirror serves as a deflection means.
The underlying object of the invention is to configure and refine an apparatus of the species in such a way that acoustic emissions of objectionable sound sources in the optical beam path of a microscope can be efficiently damped without thereby influencing the optical beam path. Also to be described is a corresponding microscope having a suitable apparatus.
The aforesaid object is achieved, with reference to the apparatus, by the features of claim 1. The coordinated claim 17 achieves the object with reference to a microscope, utilizing the apparatus according to the present invention.
The apparatus according to the present invention is characterized in that the housing, preferably the opening of the housing, is embodied and/or configured in such a way that the sound emerging, without soundproof windows, from the housing is largely extinguished by destructive interference without thereby influencing the optical beam.
What has been recognized according to the present invention is that the objectionable sound that occurs in microscopes having rapidly moving components in the beam path can be eliminated but at least contained, in an ingenious and astonishingly simple manner, by the fact that the housing, preferably the opening thereof, is configured in such a way that the sound otherwise emerging from the housing is largely extinguished by destructive interference without thereby influencing the optical beam path. This contrasts with the previously recited existing art according to which entirely passive measures are provided for, namely encapsulation of the sound-emitting components.
It is essential with respect to the present invention that the action relating to acoustic insulation has no effect on the optical beam. The latter can pass unimpeded through the opening or openings of the housing even though the sound is eliminated, but at least very considerably reduced, as a result of interference conditions.
The elimination or reduction of sound according to the present invention is possible in particular when the sound source is an acoustically monochromatic sound source (such that the sound generated has a single frequency, possibly with overtones), as is the case in a scanning microscope having a resonantly oscillating mirror. The reason is that in this case the resulting sound has substantially the frequency component of the resonant oscillating frequency.
As in the existing art, an acoustic insulation housing, hereinafter called a “housing,” is provided, the housing comprising at least one opening for beam entrance and/or beam exit. An optical entrance opening and an optical exit opening is provided in ordinary fashion in the housing, and both openings can be damped with reference to acoustic emission in accordance with the same (inventive) principle, namely utilizing destructive interference.
Concretely, it is advantageous if the opening is constituted by a tube extending away from the housing, such that sound damping takes place along the length of the tube.
In very particularly advantageous fashion, the tube is equipped with at least one tube branch protruding laterally from the tube, such that the tube branch can be embodied in the manner of a blind hole. The length of the tube branch is advantageously selected so that sound waves that run into the tube branch and are reflected therein at the end experience a phase change of 180° with respect to the wave running straight ahead, and thus together with the wave running straight ahead in the tube result in destructive interference. The effective length of the tube branch can thus be a quarter, or an odd multiple of a quarter, of the acoustic wavelength.
For maximum sound suppression, the intensity of the two waves, i.e. the intensity of the wave running straight ahead in the tube and the intensity of the wave coming back out of the tube branch, should be identical if possible, but at least similar. It is of further advantage if the tube is equipped with two or more tube branches protruding laterally from the tube, on the one hand in order to magnify the sound-eliminating effect and on the other hand to eliminate sound of different wavelengths, caused for example by different movable components or overtones.
It has already been mentioned previously that the tube branch is closed at the end, a sound reflection wall preferably being embodied there.
The absorption behavior or reflection behavior can be influenced, for example, by tuning the respective tube branch, specifically by adapting the width/diameter and/or length of the tube branch. To modify the length of the tube branch it is possible, in additionally advantageous fashion, to provide a sound reflection wall that modifies the depth of the tube branch; said wall can be carried or constituted by an adjusting screw threadable into the end of the tube, or by an adjustable/insertable adjusting pin, adjusting rod, or adjusting piston. What is ultimately important is that the tube branch be adjustable in terms of length or depth, thereby making possible tuning of the tube branch to the particular sound frequency.
Adjustment and thus tuning of the interference conditions in the tube branch can be accomplished manually, but also in motorized fashion or hydraulically or pneumatically. What is essential here is that even in a context of a change in sound frequency, an optimum adaptation or adjustment is possible in order to implement destructive interference. It is thus conceivable, for example, to perform an automatic readjustment, specifically if the frequency is constantly changing due to differing operation and constant adaptation is necessary. Automated operation is possible in any event with corresponding detection of the parameters.
Alternatively or additionally, tuning of the tube branch in order to generate the necessary destructive interference can be accomplished by selection of a suitable material for the tube/tube branch, the suitable material having a defined sound absorption behavior. Both the geometry of the tube branch and the material can be employed and thus utilized for tuning of the tube branch.
As already mentioned previously, the tube can encompass one or more tube branch(es). Alternatively to the embodiment discussed above, it is possible for the tube branch to be embodied as a bypass, proceeding from the tube and opening back into the tube, having an adapted acoustic wavelength. In very particularly advantageous fashion, the bypass has an acoustic path length that is longer than the tube by an amount equal to half the sound wavelength. This, too, ensures that destructive interference occurs.
In principle, the sound can also be “picked off” in the same fashion from a different location in the interior of the housing and combined, with a corresponding phase delay, with the sound in the opening used by the light path, so that destructive interference occurs.
With reference to the housing and to the tubes proceeding from the housing for definition of the respective openings, it is further advantageous if further (supplementary) measures for damping the objectionable sound are provided. It is possible for this purpose to provide, in the interior of the housing and/or in the interior of the tubes (and optionally the tube branches), acoustic absorbers that at least partially line the respective inner surfaces. Especially for variable-frequency sound sources, it is ideally possible to use a tube lined internally with sound-absorbing material as an optical opening of the housing, without thereby influencing the optical beam path. The provision of an absorber material embodied in the interior of the housing and in a very long tube can be viewed as an alternative to destructive interference, namely along the lines of a tube as a broad-band absorber. Such a lining also has aspects according to the present invention with regard to destructive interference: because the sound propagates at the edge of the tube more slowly, or at least at a different speed, than in the center as a result of the properties of the absorber material, the phase delay of the sound components proceeding at the edge as compared with the sound components proceeding in the center allows the formation, in particular after mixing of the two components over a longer travel distance, of a destructive interference that ultimately once again results in noise suppression toward the outside, namely analogously to the teaching of the present invention.
There are various ways of advantageously embodying and refining the teaching of the present invention. The reader is referred, for that purpose, on the one hand to the claims subordinate to claim 1, and on the other hand to the explanation below of the preferred exemplifying embodiments of the invention with reference to the drawings. In conjunction with the explanation of the preferred exemplifying embodiments of the invention with reference to the drawings, an explanation will also be given of generally preferred embodiments and further developments of the teaching.